The present invention relates to an image pickup apparatus for an electronic endoscope, and more particularly, to an image pickup apparatus which has a solid-state image sensor and is capable of properly adjusting a drive voltage for driving the solid-state image sensor.
In general, a television camera and a video camera utilize an image pickup apparatus having a solid-state image sensor such as a CCD (charge coupled device). In addition, it is well known that an electronic endoscope (which is also called an electronic scope) utilizes an image pickup apparatus having a solid-state image sensor for observation and photographing operations which is disposed at the distal end thereof. Further, there is known an image pickup apparatus in which an image pickup unit having a solid-state image sensor and a signal processor are separately provided and electrically connected by means of signal cables therebetween in order to reduce the size of the camera head. More particularly, electronic endoscopes of this type include a solid-state image sensor disposed at the distal end of the insertable portion of the endoscope and a control unit for the image sensor (separately provided from the image sensor which is detachably connected to the endoscope by means of a connector.
However, some of the drive signal voltages used to drive the solid-state image sensor need to be adjusted to match the particular image sensor used and thereby ensure that proper image signals will be obtained. Accordingly, the control unit must be adjusted to meet the requirements of signal voltages for the particular solid-state image sensor being used. The adjustment must be made whenever the endoscope is interchanged (i.e., whenever the control unit is connected to a different image sensor) To solve this problem, a prior art image pickup apparatus utilizes an adjusting resistor disposed in a connector or an operating portion of the endoscope which resistor has been previously adjusted, as disclosed in, for example, USP 4,539,586 and Japanese Laid-Open Patent Application Sho 60-244,161.
However, many different drive signals are required for a solid-state image sensor with the result that a number of the endoscope signal cables extend from the operating portion to the distal end thereof. This is disadvantageous because it is necessary to make the diameter of the endoscope as small as possible. To overcome this problem, it is possible to dispose a generator circuit for a drive signal voltage adjacent to a solid-state image sensor so as to generate a required signal at the distal end of the endoscope so that the number of signal cables from the control unit to the distal end can be reduced. Even in this case, however, it is necessary to adjust the drive voltage because the requirements of each solid-state image sensor varies. When an adjusting resistor is arranged adjacent to the distal end as in the prior art, it disadvantaneously increases the distal end in size.